feat(FN-000): run workflow work items through runtime

Fusion-Task-Id: FN-000

docs/plans/workflow-owned-merge-stack/s05-runtime-work-item-driver.md

@@ -0,0 +1,46 @@
+---
+title: "S05: runtime work-item driver"
+type: refactor
+status: draft-stack-handoff
+date: 2026-06-09
+slice: S05
+milestone: "Runtime"
+origin: docs/plans/2026-06-09-003-refactor-workflow-owned-merge-full-migration-slices-plan.md
+stack_base: feature/workflow-owned-merge-s04-builtin-ir-regions
+---
+
+# S05: runtime work-item driver
+
+## Stack Role
+
+This draft PR reserves the S05 review slot in the workflow-owned merge,
+retry, scheduling, and recovery migration stack. It is intentionally a handoff
+artifact, not the completed implementation for this slice.
+
+## Milestone
+
+Runtime
+
+## Depends On
+
+S1 workflow work items, S3 generic scheduler claim path, and S4 built-in IR regions.
+
+## Goal
+
+Let WorkflowTaskRuntime start from a workflow work item and persist node/work-item outcomes.
+
+## Expected File Scope
+
+packages/engine/src/workflow-task-runtime.ts; workflow graph executor and node handler files; runtime tests.
+
+## Expected Tests
+
+Runnable completion, retrying work creation, manual hold creation, restart resume, and duplicate lease refusal.
+
+## Exit Gate
+
+Runtime can progress workflow work without old merge queue callbacks.
+
+## Full Plan
+
+See `docs/plans/2026-06-09-003-refactor-workflow-owned-merge-full-migration-slices-plan.md`.